This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A189568 #9 Mar 19 2017 16:23:40 %S A189568 1,1,2,6,24,80,326,1566,9544,65036,518498,4750006,48830634,554929274, %T A189568 6926227324,93970452970,1377573324202 %N A189568 Number of permutations p of 1,2,...,n satisfying |p(i+3)-p(i)|<>4 and |p(j+4)-p(j)|<>3 for all i=1..n-3, j=1..n-4. %C A189568 a(n) is also the number of ways to place n nonattacking pieces rook + leaper[3,4] on an n X n chessboard. %H A189568 V. Kotesovec, <a href="https://oeis.org/wiki/User:Vaclav_Kotesovec">Number of ways of placing non-attacking queens, kings, bishops and knights</a> (in English and Czech) %F A189568 Asymptotic: a(n)/n! ~ 1/e^4. %Y A189568 Cf. A137774, A189358, A189563, A189564, A189565, A189566, A189567. %K A189568 nonn,more,hard %O A189568 0,3 %A A189568 _Vaclav Kotesovec_, Apr 23 2011